ALKALINE EXTRACTION INITIATED OZONE BLEACHING OF KRAFT PULP

摘要

A multi-stage process is disclosed for the bleaching and delignification of lignocellulosic pulps which comprises the following steps in sequence: (a) extracting a lignocellulosic pulp slurry with alkali while maintaining the slurry pH above about 10; (b) washing the pulp slurry with an acid at a pH below 3 whereby the heavy metal cations are removed from the lignocellulosic pulp slurry in order to avoid detrimental effects during succeeding bleaching stages; (c) passing a stream of ozone through the pulp slurry while maintaining the slurry pH below about 5; (d) extracting the pulp slurry with alkali while maintaining the pH of the slurry from about 7 to about 10; and (e) passing a stream of ozone through the pulp slurry while maintaining the slurry pH below about 5.